The invention relates to interfaces between cellular telephones and modems of the kind used in conjunction with personal computers, particularly portable or "laptop" computers.
With the widespread availability of portable personal computers, low-cost modems, and cellular telephones, the infrastructure necessary for convenient mobile data communication would seem to be in place. The primary obstacle is the difficulty of integrating these components. Modems of the kind typically used with personal computers are intended to physically and electrically interface with the land-based telephone network, not cellular telephones. Cellular telephones, primarily intended for voice communication, often lack data input and output.
Partial solutions for this integration problem exist. One known solution is to eliminate the need to interface with a cellular telephone by providing a wireless modem with an integrated cellular transceiver. This solution is undesirable from a cost standpoint since the hardware necessary for cellular communication is relatively expensive and a user may end up purchasing both a cellular modem and a cellular telephone at great expense and furthermore pay duplicate monthly cellular service fees.
Another known solution is to provide a cellular telephone with a customized data interface intended to interoperate with a special modem installed within the portable computer. One problem with this approach is that the special modem designed for use with the cellular telephone cannot be used over conventional telephone lines, necessitating ownership of at least two modems. Another problem is that special software is required to operate the special cellular-compatible modems. Widely available communication software as well as software intended to run on-line services cannot be used.
Yet another known solution is to provide a hardware interface in a separate physical package which simulates a landline RJ-11 telephone jack to a conventional modem and connects to the data input/output of a cellular telephone. The user, already burdened with carrying a computer and telephone, must then carry this interface also. The interface or the cellular telephone must be able to generate a high-voltage ring signal for input to the modem. Furthermore, modem signals may degrade within this interface, potentially resulting in a loss of data before the cellular network is even reached.
What is needed is simple hardware for integrating cellular telephones and portable personal computers to provide a low-cost and reliable wireless data communication capability. The hardware should support widely-available communications software and should also permit data communication via the conventional telephone network.